In this chapter, we covered the basics of the MQTT protocol and some of its strengths and weaknesses. We have seen how we can use it in our sensor, actuator, and controller projects as a simple means to cross firewall boundaries.

In the next chapter, we will introduce the XMPP protocol and some of the new communication patterns it allows such as federation, global identity, presence, friendship, authorization, delegation of trust, provisioning, and so on. We will also show how these patterns can help us build a secure architecture for Internet of Things.